Our closest neighboring star was discovered a century ago. Ever since then, astronomers have suspected that it’s a member of a triple star system. And some recent research provides confirmation of that idea.

Despite its nearness, Proxima Centauri is so feeble that it’s invisible to the unaided eye. That’s why astronomers didn’t spot it until 1915. Today, we know that it’s just four-and-a-quarter light-years from Earth.

At the time of its discovery, astronomers noticed that Proxima Centauri was at nearly the same distance as a much brighter star — actually a pair of stars whose light blends together to make it the third-brightest star in the night sky.

This brilliant double star is Alpha Centauri. It’s only about a tenth of a light-year farther than Proxima, and it moves through space at nearly the same velocity as Proxima. So from the beginning, astronomers have suspected that Proxima Centauri is part of the Alpha Centauri system.

But Proxima is a long way from the other two stars. If it is bound to them, it must have almost exactly the same speed through space. Otherwise, the little star would escape Alpha Centauri’s gravitational grip.

Recent measurements of Proxima Centauri’s motion have shown that the star is indeed bound to the binary. It orbits its bright partners once every 550,000 years.

So the nearest star system to the Sun is triple, harboring two bright stars plus dim little Proxima.